President Trump warned European leaders Friday that they “better watch themselves” because a wave of immigration is “changing the culture” of their countries.

“I think it’s a very negative thing for Europe. I think it’s very negative,” Trump said. “And I know it’s politically not necessarily correct to say that, but I’ll say it and I’ll say it loud.”

Trump’s comments came during a joint news conference with British Prime Minister Theresa May in Ellesborough, England. Trump was asked to elaborate on comments published Thursday in the British tabloid the Sun in which he said an influx of migrants fleeing violence and seeking asylum had “changed the fabric of Europe.”

In his remarks Friday, Trump blamed immigration for terrorist attacks and offered Germany as an example.

“I have a great relationship with Angela Merkel,” Trump said, referring to the German chancellor. “But I think that’s very much hurt Germany. I think it’s very much hurt other parts of Europe.”

He appeared to be referencing a wave of refugees who have entered Europe from Syria and other unstable parts of the Middle East and North Africa.

“I think they better watch themselves because you are changing culture, you are changing a lot of things, you’re changing security,” Trump said of European leaders. “Look at what’s happening. I mean, you take a look at what’s happening to different countries that never had difficulty, never had problems. It’s a very sad situation. It’s very unfortunate.”

At the news conference, May was asked if she concurred with Trump’s assessment.

“The U.K. has a proud history of welcoming people who are fleeing persecution to our country,” she told reporters. “We have a proud history of welcoming people who want to come to our country to contribute to our economy and contribute to our society. And over the years, overall, immigration has been good for the U.K. It’s brought people with different backgrounds, different outlooks here to the U.K.”

May also said that it is important for the United Kingdom to “control our borders.”

“What is important is that we have a set of rules that enables us to determine who comes into our country,” she said. “And, of course, that is what, as a government, we have been doing for number of years and will be able to continue to do in the future.”

Trump also repeated criticism of U.S. immigration laws, which he unsuccessfully lobbied the Republican-controlled Congress to change.

“We have laws that are so bad I don’t even call them laws,” Trump said. “It’s just like you just walk across the border. You walk across the border, you put one foot on the land, and now you’re tied up in a lawsuit for five years. It’s the craziest thing anyone’s ever seen.”